This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Projection systems create video images by varying the color and shade of projected light. One example of a projection system is a Digital Light Processing (“DLP”) system. DLP systems employ an optical semiconductor, known as a Digital Micromirror Device (“DMD”) to project video onto a screen. DMDs typically contain an array of at least one-half million or more microscopic mirrors mounted on microscopic hinges. Each of these mirrors is associated with a point on the screen, known as a pixel. By varying the amount of light that is reflected off each of these mirrors, it is possible to project video images onto the screen.
Electrically actuating each of these hinge-mounted microscopic mirrors, it is possible to either illuminate a point on the screen (i.e., “turn on” a particular micromirror) or to leave that particular point dark by reflecting the light somewhere else besides the screen (i.e., “turn off” the micromirror). Further, by varying the amount of time a particular micromirror is turned on, it is possible to create a variety of gray shades. For example, if a micromirror is turned on for longer than it is turned off, the pixel that is associated with that particular micromirror will have a light gray color; whereas if a particular micromirror is turned off more frequently than it is turned on, that particular pixel will have a darker gray color. In this manner, video can be created by turning each micromirror on or off several thousand times per second. Moreover, by shining colored light at the micromirrors instead of white light, it is possible to generate millions of shades or color instead of shades of gray.
As technology improves, the demand for high resolution imaging may increase. Currently there are many imaging formats, such as 1080p, 1080i, 720p, 480p or 480i. The resolutions of each of these standards vary. For example, the 1080i standard employs more than two million pixels to display an image. Producing DMDs with sufficient numbers micromirrors to support higher resolution images (e.g., 2 million micromirrors) may be expensive. For this reason, as described in greater detail below, several techniques have been developed to facilitate the display of pixel resolutions in excess of the number of micromirrors on a given DMD.
In a conventional system, the DMD contains an orthogonal grid of micromirrors arranged in rows and columns. The total number of pixels displayed on the screen is the number of rows of micromirrors on the DMD multiplied by the number of columns. (i.e., there is a 1 to 1 correspondence between the number of micromirrors on the DMD and the number of pixels displayed).
However, because the cost of a DMD in a projection system is proportional to the number of micromirrors on the DMD, it is beneficial for a single DMD to display more than one pixel on the screen. One technique for enabling this is to redirect the light reflected from the DMD to more than one point on the display screen. Typically, this is performed by a mechanically actuated projecting lens that can shift between two or more projection positions. For example, the projecting lens may first direct light from one of the micromirrors on the DMD to the display screen at a first pixel position. After the first pixel has been displayed for a given time, the projecting lens may be actuated to shine light from the same DMD micromirror at the second pixel position. The projecting lens alternates rapidly between the two positions to display each respective pixel. The result is a first and a second pixel displayed in separate positions on the display screen.
For example, an actuator may be configured to redirect the light to display the second pixel at a position to the right or left of the first pixel. Similarly, an actuator may also be configured to redirect the light to display a second pixel at a point above or below the first pixel location. Moreover, by adding a second actuator, the projecting lens assembly may be able to shift in both the horizontal and vertical directions. In other words, using two actuators allows a single micromirror on the DMD to display additional pixels in both the horizontal and vertical directions, doubling the resolution possible from a single actuator. However, the addition of a second actuator is more expensive than a single actuator system. Increasing the display resolution from a single actuator is desirable.